Known in the art a number of processes for the preparation of mangiferin. One of the processes consists in that from the disintegrated serial part of a plant belonging to the genus of Hedysarum alpinum L. xanthone glycosides are extracted with 80% ethanol. The extraction is effected upon heating at reflux on a water bath. The starting material and the extraction agent are taken in the amount of 1 kg of the starting plant material per 10 liters of the extraction agent. The resulting extract is partly evaporated. The evaporated extract is treated with water and then purified by chloroform. As a result two layers are formed, wherefrom the upper one contains xanthone glycosides. The layers are separated. From the upper layer mangiferin is isolated chromatographically on a polyamide. To this end, the upper layer is placed into a column and eluted with an ethanol-water mixture. The ethanolic eluates containing mangiferin are evaporated and recrystallized from a mixture dioxane-water (volume ratio of 1:1). The yield of mangiferin produced by this process is 0.5% by weight of the starting material (see V. B. Kuvaev, V. I. Glysin, G. S. Glysina, A. I. Ban'kovsky "Vegetable Resources", 1972, vol. 8).
This process results in the production of mangiferin of a sufficiently high purity grade. However, the use of sorption techniques for separation and purification of xanthone glycosides in the above process hinders the preparation of mangiferin and makes it economically inefficient.
Also known in the art is another process for the production of mangiferin. In this process from the disintegrated aerial portion of a plant of the species Hedysarum alpinum L. or Hedysarum flavescens Rgl. et Schmalh. xanthone glycosides are extracted by means of aqueous 80% ethanol for several times (up to four) at the temperature of 70.degree. C. The combined extracts are evaporated. After the filtration the evaporated extract is placed into a division funnel and treated with a non-polar solvent such as chloroform. This operation is carried out for the purification of the extract from chlorophyll and other non-polar compounds contained in the vegetable stock. As a result, two layers are formed. The layers are separated. The upper aqueous layer contains xanthone glycosides. Then the upper layer is placed into a funnel, added with butanol, the mixture is stirred and allowed to stratify. The butanolic layer (upper) comprising a solution of xanthone glycosides in butanol is separated. This extraction of xanthone glycosides is carried out for several times. The combined butanolic solutions are evaporated to a predetermined volume so that mangiferin precipitates. The resulting mangiferin is recrystallized from a mixture of solvents--dioxane-water at the volume ratio thereof of 1:1. The yield of mangiferin in this process is 0.66% by weight of the starting vegetable stock (cf. S. V. Rusakova, V. I. Glysin, S. I. Kocherga, O. V. Soldatova, V. M. Mulevich, USSR Inventor's Certificate No. 596242 of Nov. 15, 1977).
One of the advantages of this process resides in replacement of a complicated and expensive chromatographic equipment for isolation of mangiferin by a liquid-phase extraction with an organic solvent. This has made it possible to increase the yield of mangiferin. However, its yield is still insufficient. This is due to the fact that during extraction of xanthone glycosides with butanol accompanying compounds, i.e. flavonol-O-glycosides also pass into the extract along with mangiferin. The presence of these compounds in the extract hinders separation of mangiferin from the evaporated butanolic solution. Furthermore, the process necessitates a repeated extraction of the vegetable stock with 80% ethanol.
Known is a process for extraction of xanthone glycosides from plants of the genus of Hedysarum by means of a mixture of acetone and water. In this case the process of extraction proceeds rather rapidly without application of an elevated temperature (cf. Proceedings of the All-Union Conference on Extraction, "Zinjate" Publishing House, Riga, 1977).
The plants Hedysarum alpinum L. and Hedysarum flavescens Rgl. et Schmalh. are described in the official publication "Flora of the USSR" compiled by E. G. Bobrov et al and published by Izdatelstvo Akademi Nauk SSSR Publishers, Moscow/Leningrad (1948). On page 278 of this publication Hedysarum flavescens Rgl. et Schmalh., identified in 1881, is described as a yellowish plant of height up to 1.5 m. The plant is almost bare and except for several enlargements, the stalks are straight or slightly ascendenent and cylindrical. The stipules are scaly, joined with one another in lower leaves and free in upper leaves. The leaves have very short stalks and are arranged in 3 to 5 pairs, elongated egg-shaped or elliptical 20-35 (45) mm long, 17-20 (35) mm wide, rounded or obtuse at the vertex, with pointed ends. Floriferous shoots (together with raceme) are much longer than the leaves. The racemes are not thick, they have 15-35 flowers all being one-sided. The bracts are longer than the flowers before the blooming so that all racemes (in buds) look like a pappus. The bract cup is shorter than the peduncle at the end. The peduncles are thin, 3 to 5 mm long. The flowers are 15-20 mm long. The cup is bell shaped and the teeth of the cup are unequal: the lower teeth are longer than the cup tube and the upper ones are shorter. The corolla is yellow. The carpel of the flag is elongated or elongated and elliptical, slightly recessed at the vertex. The cover slip is longer than the flag and wings. The ovary is downy, on a long stem, with a few seed buds. The beans are on a stem with 2 to 4 flat segments which are elongated and elliptical or elongated, thin and reticular, having a wide integral wing at the edge and narrowing to the base. The pods are bud-like and flattened.
The plant is found in mixed-grass cereal plains, subalpine meadows, along banks of mountain rivers and at glaciers; predominantly in the subalpine zone at an altitude of 2500 to 3200 m.--location Mid. Asia. The type is in Legingrad.
The plant is valuable as an animal feed.